Process of controlled radical grafting of a polyolefin

ABSTRACT

The present invention relates to a controlled radical grafting process of a polyolefin derived from monomeric units including α-olefins. This process comprises the reaction of the polyolefin and at least one radical reaction initiator with a grafting system which comprises at least one grafting compound having an electron donator heterocyclic aromatic ring conjugated to at least one —HC═CR 1 R 2  group in which at least one of R 1  and R 2  is an electron acceptor functional group. The process can be performed continuously in an extruder or discontinuously in a mechanical mixer.

This is a National Stage entry of International ApplicationPCT/IB2004/002098, with an International Filing Date of Jun. 24, 2004,which was published as WO 2004/113399 A3, and the complete disclosure ofwhich is incorporated into this application by reference.

BACKGROUND OF THE INVENTION

The invention relates to a controlled grafting process of a polyolefinin the presence of radical reaction initiators.

Radical grafting of polyolefins is a method widely used in theindustrial field for the production of modified materials, essential inmany plastics formulations and used, for example, as chemical couplingagents, impact modifiers or compatibility enhancers for fillers. Thegrafting reaction allows the introduction into the polymeric chain ofsmall quantities of polar groups, for example of anhydride or acid esternature (contained in general in small percentages by weight), with theobject of imparting new properties to the polymer without significantlyvarying its starting characteristics. Usually, the reactivetransformation process is conducted in discontinuous mechanical mixersor in extruders, at a temperature which makes it possible to maintainthe reaction mixture in the molten state.

The reactive mixture also comprises, beyond the polyolefin, at least oneradical reaction initiator and at least one grafting compound. Usually,the initiator is a peroxide, whilst the grafting compound, possibly inmixture with other compounds, is an unsaturated polar compound, such as,for example, maleic anhydride, a maleic ester, a maleic semiester or amethacrylate.

In the reaction mechanism the radical reaction initiator, a peroxide,decomposes into peroxide radicals (RO′) at high temperatures. Theperoxide radicals can be stabilised with termination reactions, combinedwith a grafting compound (M) or extract a hydrogen from the polyolefin(P) by generating macroradicals (P.). The macroradicals (P.) of thepolyolefin can give cross linking products, degradation products orinteract with grafting compounds to give other radicals (PM.). Thegrafted polyolefins (PMH) are generated when the macroradicals (PM.) ofthe grafted polyolefin become stable by extracting a hydrogen fromanother molecule of polyolefin, which in turn becomes radical (P.).

However, because of the great reactivity and consequent low selectivityof the free radicals in their reactive activity, the grafting of thepolyolefin occurring in the melt by radical means is accompanied bycollateral reactions which can be attributed to the degradationreactions and to cross linking reactions of the polyolefin. When thesereactions occur, which compete with the grafting, the process thereforehas a reduced overall efficiency and a final product with a low degreeof grafting. Another consequence of the degradatory and cross linkingreactions is the variation in the average molecular weight of thepolyolefins.

In the treatment of polypropylene with peroxides, for example, thephenomenon of rupture of the macromolecular chain through β-splittingreactions is predominant. The macroradical coupling reactions which leadto the formation of cross linked polymers are, in fact, notably slowerthan β-splitting because of both the ratio between the velocityconstants of the two processes, which promotes degradation, and of thebiomolecularity of the kinetics of the coupling process. The overalleffect of the addition of a peroxide to polypropylene therefore leads toa diminution of the average molecular weight and an increase in the“melt flow rate” (MFR) with strong variations in the primary structureof the polymer.

The association of maleic anhydride (MAH) in the treatment of thepolypropylene with peroxides to obtain grafting of the polymer leads tosimilar results. In fact, a drastic reduction in the molecular weight isevident for any grafting compound/initiator ratio and a dependence ofthe degree of final grafting on this ratio is evident. It is known,moreover, that the coupling of the MAH takes place principally on theprimary radical deriving from the β-splitting reactions.

By working in the melt, therefore, it is rather difficult to obtain agood compromise between the radical grafting reactions and theβ-splitting reaction of the polymeric chain. The problem is essentiallytied to the formation of unstable tertiary macroradicals which give risepreferentially to β-splitting reactions.

To limit the degradatory effect and, therefore, the β-splittingreactions, radical grafting procedures are known (referred in particularto the grafting of polypropylene) which utilise molecules or systems ofmolecules to put along-side known grafting compounds and which are ableto convert the macroradicals into radicals less subject to β-splittingreactions.

One example is the radical grafting assisted by styrene (STY). In thegrafting of polypropylene (PP) with glycidyl methacrolate (GMA),slightly reactive to macroradicals of the polymer, the styrene can beutilised as a grafting co-agent. The styrene reacts in the first placewith the macroradicals of polypropylene giving rise to radicals of themore stable styrilic type less subject to the degradation reaction.Subsequently these radicals co-polymerise with GMA. In this way, insteadof directly grafting the GMA on the polymeric chain, the STY is insertedas a bridge between the PP and the grafting compound. It is deemed,moreover, that GMA reacts more easily with the styrilic radicals, thanwith macroradicals of PP: consequently, a synergic effect takes placewhich further limits the degradation of the polymer.

Similar results are obtained although with different reaction mechanismsby utilising styrene in the radical grafting of polypropylene withmaleic anhydride.

The use of the styrene as grafting co-agent is limited, however, by thefact that only some grafting compounds succeed in effectivelycopolymerising with the styrilic macroradicals with effective inhibitionof the degradatory processes. The procedure is only useable, however, toinsert some functional groups into the polyolefin chain, limiting thepossible applications of the final grafted products.

SUMMARY OF THE INVENTION

The principal object of the process according to the present inventionis that of obviating the criticality and limits of the known proceduresfor radical grafting of polyolefins.

A further object is that of improving the efficiency of the graftingreaction of polyolefin by discouraging the collateral reactions whichcompete with the main grafting reaction.

This and other objects and advantages are achieved by the radicalgrafting process of a polyolefin comprising the reaction of thepolyolefin and at least one radical reaction initiator with a graftingsystem which comprises at least one grafting compound having an electrondonating heterocyclical aromatic ring conjugated to at least one—HC═CR₁R₂ group in which at least one of the R₁ and R₂ is an electronacceptor functional group.

As already indicated in the known processes, in the case ofpolypropylene radical peroxides attack on the macromolecules causes theformation of unstable tertiary macroradicals which evolve preferentiallythrough β-splitting reactions. The combination of macroradicals withgrafting compounds, such as, for example, maleic anhydride, leads tomore unstable radicals. The criticality of the grafting reactiontherefore resides in the instability of these intermediate macroradicalswhich discourage the reactions which lead to the formation of stablepolypropylene molecules (grafted) from these macroradicals combined withthe grafting compounds.

The process according to the present invention makes it possible toregulate the reactivity of these tertiary macroradicals by increasingtheir stability and at the same time reducing the tendency to evolvethrough degradation reactions.

This result is obtained by utilising, as grafting compounds, compoundswith a molecular structure comprising an electron donator heterocyclicaromatic ring conjugated to at least one group of formula

which has a double bond, in which at least one of the two substituentgroups R₁ and R₂ is an electron acceptor functional group.

The electron acceptor group permits attachment on the double bond of thegrafting compound by the tertiary macroradicals, whilst the electrondonator heterocyclic aromatic ring stabilises by resonance the newmacroradical which forms.

The high speed of addition of the macroradicals to the graftingcompounds (due principally to the electron acceptor character of thesubstituent groups on the double bond) and the formation of a radicalstabilised by the conjugation with the heterocyclic aromatic ringexplains both the hydrogen extraction reactions, which leads to stablemolecules of grafted polyolefin, and the occurrence of couplingreactions between radicals, with formation of cross linked/branchedpolyolefin. Consequently, there is an inhibition of the degradativeβ-splitting reactions.

In some cases the stable molecules of grafted polyolefin, deriving fromthe polyolefin/grafting compound macroradicals stabilized by loss of ahydrogen, still have a double bond. These molecules can thereforecombine with other grafting compounds thanks to the unsaturation (doublebond). In the formulation of the grafting system according to theinvention it is therefore possible to associate also grafting compoundsused in the processes according to the prior art, such as maleicanhydride, maleic esters, acrylic and methacrylic compounds such asglycidyl methacrylate or azide derivatives. The functionality of thesecompounds can insert on the polyolefin stabilised by grafting compoundswith a heterocyclic aromatic ring.

Thanks to the use of a grafting system comprising grafting compoundswith adequate substituent polar groups, to their speed of addition, aswell as to their capacity to give life to macroradicals stabilised byresonance, the process according to the present invention thereforemakes it possible to contain the degradation of the polyolefin and atthe same time to graft on chain functional groups suitable for thesubsequent use of the product, for example as a compatibility enhancingagent, chemical coupling agent or impact modifier.

The heterocyclic aromatic ring of grafting compounds utilised in theprocess according to the invention can be preferably chosen from afuranic, thiophenic or pyrrolic ring, possibly substituted.

The substituent functional groups on the double bond, previouslyindicated R₁ and R₂, can advantageously be chosen, on the other hand,between the group consisting of —H, —COOR, —COOH, —COR, —COH, —CN,—CONH₂, —COO(CH₂)_(n)CF₃ and —COO(CH₂)_(n)CN, where R is a linear orbranched aliphatic or aromatic alkyl group and n is a whole numberbetween 1 and 20 with the proviso that R₁ and R₂ are not both —H.

Preferred examples of grafting compounds according to the presentinvention are, for example, the following compounds:

-   -   3-carboxyethyl 2-furfuryl acrylate of ethyl (CEFA)

which has a furanic ring as a heterocyclic aromatic ring and —COOR as asubstituent group both for R₁ and for R₂, with R=Et, where Etcorresponds to —CH₂CH₃;

-   -   Ciano 2-furfuryl acrylate of ethyl (CFA)

which has a furanic ring as a heterocyclic aromatic ring, the group —CNas a substituent for R₁ and the group —COOR as substituent group for R₂,with R=Et, where Et corresponds to —CH₂CH₃; and

-   -   butylic ester of 3-(2-furanyl)-2-propenoic acid (BFA)

which has a furanic ring as a heterocyclic aromatic ring, R₁ is —H andR₂ is —COOR, where R corresponds to —CH₂CH₂CH₂CH₃.

The process according to the present invention can be performeddiscontinuously with a single mixer or continuously with a singleextruder.

The discontinuous (batch) process can be performed according to thefollowing stages:

-   -   preparation of the mixing/reaction chamber into the process        conditions;    -   introduction of the polyolefin into the mixer;    -   melting and mechanical mixing of the polyolefin;    -   introduction of the grafting system into the mixer;    -   homogenisation of the mixture of polyolefin/grafting system    -   introduction of the radical reaction initiator into the mixture;    -   grafting reaction of the polyolefin; and    -   (possible) introduction of a radical reaction inhibitor.

Initially, the reaction chamber of the mixer or extruder, preferablyfilled with inert gas, for example nitrogen, is brought to the processtemperature. Polyolefin is then introduced into the mixture inquantities such as to fill the mixing chamber; during the melting of thepolymer, still in an inert gas atmosphere, mechanical mixing takes placewhich allows homogenisation of the material. The melting and mixing ofthe polymer can be considered complete when the torque transmitted bythe rotor of the mixture is stabilised. The grafting system is added tothe polyolefin and process proceeds, still under an inert gasatmosphere, to the homogenisation of the mixture. Once adequate mixinghas been reached, which can be evaluated by the variation in time of thetorque of the rotor, the radical reaction initiator is introduced. Then,the true and proper radical reactive grafting stage of the polyolefinfollows. In order to block the progress of the reaction beyond theestablished limits it is possible to add to the reagent mixture aradical reaction inhibitor compound such as 3,5-di-tert-butyl-4hydroxytoluene (BHT), Irganox 1010 or Irganox 1076.

Advantageously the overall residence time of the polyolefin in the mixerlies between 5 and 30 minutes, whilst the process temperature liesbetween 120 and 230° C. and the mixer rotor has angular velocity between20 and 70 rpm.

The continuous process can advantageously be performed in a twin screwextruder. Preferably, the polyolefin is introduced into the firstsection of the extruder whilst the remainder of the reagents are fedinto the subsequent section. The average temperature in the reagentintroduction section of the extruder must reach at least 210° C. Byusing, for example, an extruder of diameter D=35 mm and length/diameterratio L/D=40 advantageously the flow rate can be maintained at 200 kg/h.

The reagent mixture in the process according to the invention preferablyhas the following composition:

-   -   100 parts by weight of a polyolefin chosen from the group of        homopolymers of α-olephins and ethylene/α-olefin copolymers;    -   from 0.05 to 5 parts by weight of a radical reaction initiator        or a mixture of initiators;    -   from 1 to 25 parts by weight of a grafting system; and    -   from 0.05 to 5 parts by weight of a radical reaction inhibitor,        to be introduced possibly into the mixture at the end of the        process to block the grafting reaction.

Preferably the said radical initiator has a half life of between 10 and200 seconds in the temperature range lying between 120 and 240° C. Thesaid radical initiator can be an organic peroxide, such as a dialkylperoxide, a diacyl peroxide, a peroxyester or a peroxyketal andadvantageously can be chosen from the group consisting of dicumylperoxide, ditertbutyl peroxypropylbenzene, 2,5 dimethyl 2,5 ditertbutylperoxy-hexane, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonan andtheir mixtures.

A first advantage which can be achieved with the radical graftingprocess according to the present invention is that of strictly reducingthe alteration of the initial macromolecular structure of thepolyolefin. This result can be detected, for example, in the batchprocess, performed in mechanical mixers, by observing that the finaltorque of the grafted polyolefin is equivalent to that of thenon-grafted polyolefin.

Another advantage lies in a net improvement of the overall efficiency ofthe grafting reaction which allows final products to be obtained with abetter degree of grafting. It is possible to modulate the degree ofgrafting of the final product by acting on the composition of the feed.

The use of a grafting system with the characteristics according to thepresent invention makes it possible to control the reactivity of themacroradicals independently of the structure of the polyolefin to begrafted. The process is thus applicable to all types of polymerscontaining α-olephins.

A further advantage lies in the possibility of inserting into thepolyolefin any type of polar functional group such as, for example,ester, amide, cyloxane or ciano groups, obtaining a good degree ofgrafting. This allows an increase in the possible fields of applicationof the final products. From this point of view it is also advantageousto have the possibility of performing the process according to theinvention through reactive mixing.

The process according to the present invention further allows a highflexibility in the insertion of functional groups into the polyolefinchain. The grafting can in fact derive directly from the functionalgroups present in the compounds which permit stabilisation of themacroradicals or indirectly from known grafting compounds such as maleicanhydride able to bind to the already stabilised macroradicals.

The grafting compounds chosen for the process according to the inventionare easily available and do not require a complex synthesis process. Theapplication of this radical grafting process of the polyolefins istherefore economically advantageous.

Further advantages and characteristics of the present invention willbecome evident from the following non-limitating examples.

EXAMPLE 1

A discontinuous Brabender Plastograph OH47055 mechanical mixer with amixing chamber of 30 cm³ provided with two rotors is used. The averagetemperature was 180° C. with an overall residence time of 25 minutes.Speed of rotation was fixed at 50 rpm.

Having brought the mixing chamber to a temperature of 180° C. in anitrogen atmosphere, 100 parts by weight (20 g) of polypropylene withMFR (Melt Flow Rate) equal to 0.24 g/10 min was introduced (stillmaintaining the atmosphere of nitrogen) in such a way as to fill thechamber entirely. Having reached a constant torque, 25 parts by weightof 3-carboyethyl 2-furfuryl acrilate of ethyl (CEFA) were introduced inthe liquid state as a grafting system and, after having reached anadequate homogenisation of the mixture, 2 parts by weight of dycumylperoxide were introduced as radical reaction initiator. At the end ofthe process 1 part by weight of BHT was introduced as radical reactioninhibitor to inhibit any further radical process.

The torque transmitted by the two rotors at the end of the procedure andthe degree of grafting (FD) of the polyolefin after the process arereported. The degree of grafting (% mol) is intended to mean the numberof functional groups introduced onto the polyolefin chain each 100repeating monomeric units.

The variation of the torque, detected through continuous monitoring ofthe force exerted by the rotors during mixing is utilised to follow theprocedure of the reactions in a qualitative manner. This quantity ismoreover directly proportional to the viscosity of the molten mass whichis influenced by the addition of liquid reagents, by possible variationsin molecular weight to which the polymer is subjected and by theprogressing over time of the reaction itself. The degradation of thematerial (decrease in molecular weight) is manifest, therefore,generally through an evident decrease in the torque. At the end of theprocess in the mixing chamber only the final product is present and thefinal value of the torque is, therefore, indicative of the properties ofthe product.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   25 parts by weight of CEFA;-   2 parts by weight of DCP;-   1 part by weight of BHT.-   Final torque=3.8 Nm;

FD=0.8% mol

EXAMPLE 2 Comparison

With the mixer of example 1 and with the same process conditions thesame quantity of polypropylene was mixed, characterised by MFR (MeltFlow Rate) equal to 0.24 g/10 min, for a time of 25 minutes at averagetemperature of 180° C. and a rotation speed of 50 rpm. No other compoundwas added to the polypropylene in the mixture. For the final product thefinal torque was noted.

Final torque=10.9 Nm.

EXAMPLE 3 Comparison

Process was as in example 1 except for the fact that the grafting systemwas not introduced, only the reaction initiator DCP. For the finalproduct the final torque was noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   0.5 parts by weight of DCP;-   1 part by weight of PHD.-   Final torque=1.4 Nm.

As can be seen by comparing examples 1, 2 and 3, the polypropylenegrafted with the process according to the present invention has a finaltorque less than the propylene treated only thermally (example 2) butgreater than that demonstrated by the propylene treated only with DCP(example 3). It is possible to conclude that this is due to theinhibition action against the degredation reactions exercised by thegrafting system according to the invention.

EXAMPLE 4

Process was as in example 1, halving, however, the quantity of initiatorDCP fed to the mixer. For the final product, the final torque and FDwere noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   25 parts by weight of CEFA;-   1 part by weight of DCP;-   1 part by weight of BHT.-   Final torque=5.3 Nm;-   FD=0.4% mol.

EXAMPLE 5

Process was as in example 1, reducing however, the quantity of graftingcompound CEFA fed to the mixer. For the final product the final torqueand FD were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   10 parts by weight of CEFA;-   2 parts by weight of DCP;-   1 part by weight of BHT.-   Final torque=3.7 Nm;-   FD=0.7% mol.

EXAMPLE 6

Process was as in example 5, halving, however, the quantity of reactioninitiator DCP supplied to the mixer. For the final product the finaltorque and FD were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   10 parts by weight of CEFA;-   1 part by weight of DCP;-   1 part by weight of BHT.-   Final torque=5.3 Nm.-   FD=0.4% mol.

EXAMPLE 7

Process was as in example 5, halving, however, the quantity of graftingcompound CEFA supplied to the mixer. For the final product the finaltorque and FD were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   5 parts by weight of CEFA;-   2 parts by weight of DCP;-   1 part by weight of BHT.-   Final torque=3.2 Nm;-   FD=0.7% mol.

EXAMPLE 8 Comparison

Process was as in example 7, halving, however, the quantity of reactioninitiator DCP supplied to the mixer. For the final product the finaltorque and FD was noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   5 parts by weight of CEFA;-   1 part by weight of DCP;-   1 part by weight of BHT.-   Final torque=3.8 Nm.-   FD=0.3% mol.

By comparing examples 1 and 4 to 8, it is observed that the degree ofgrafting FD can be modulated on the basis of the supplied composition.High percentages of CEFA (grafting system) promote FD. The degree ofgrafting FD is, however, also influenced by the quantity of initiator:with the same grafting system, FD is directly proportional to thequantity of peroxide supply. It is also to be noted that the finaltorque is inversely proportional to the supplied quantity of reactioninitiator.

EXAMPLE 9

A discontinuous Brabender Plastograph OH47055 mixer was utilised with amixing chamber of 30 cm³ provided with two rotors. The averagetemperature was 180° C. with an overall residence time of 25 minutes.The speed of rotation was fixed at 50 rpm.

Having brought the mixing chamber to the temperature of 180° C. in anitrogen atmosphere, 100 parts by weight (20 g) of polypropylene withMFR (Melt Flow Rate) equal to 0.24 g/10 minutes was introduced (stillmaintaining the nitrogen atmosphere) in such a way as entirely to fillthe chamber. Having reached a constant torque, 20 parts by weight ofciano 2-furfuryl acrylate of ethyl (CFA) were introduced in the solidstate as grafting system and, after having reached an adequatehomogenisation of the mixture, 2 parts by weight of dicumyl peroxideinitiator as radical reaction initiator were introduced. At the end ofthe process, 1 part by weight of BHT was introduced as radical reactioninhibitor to inhibit any further radical process.

For the final product the final torque and FD were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   20 parts by weight of CFA;-   2 parts by weight of DCP;-   1 part by weight of BHT.-   Final torque=3.6 Nm;-   FD=0.51% mol.

EXAMPLE 10

A discontinuous Brabender Plastograph OH47055 mechanical mixer with themixing chamber of 30 cm³ provided with two rotors was used. The averagetemperature was 180° C. with an overall residence time of 15 minutes.Speed of rotation was fired at 60 rpm.

Having brought the mixing chamber to a temperature of 180° C. in anitrogen atmosphere, 100 parts by weight (20 g) of polypropylene with aMFR (Melt Flow Rate) equal to 0.8 g/10 min were introduced (stillmaintaining the nitrogen atmosphere) in such a way as to entirely fillthe chamber. Having reached a constant torque, 10.4 parts by weight ofgrafting system were introduced of which 10 parts by weight of maleicanhydride (MAH) in the solid state and 0.4 part by weight of butylicester of 3-(2-furanyl)-2-propenoic acid (BFA) in the liquid state. Afterhaving reached adequate homogenisation of the mixture, 0.4 parts byweight of 2,5 dimethyl 2,5 diterbutyl peroxy-hexane were introduced asradical reaction initiator. At the end of the process, 1 part by weightof BHT was added as radical reaction inhibitor to inhibit any furtherradical process.

For the final product, the final torque was noted and the degree ofgrafting FD relative to the introduction of the functional groups ofMAH, indicated as FD (MAH), and of BFA, indicated as FD (BFA), werenoted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   0.4 parts by weight of BFA;-   10 parts by weight of MAH;-   0.4 parts by weight of 2,5dimethyl 2,5 diterbutyl peroxy-hexane;-   1 part by weight of BHT.-   Final torque=4.4 Nm;-   FD(MAH)=0.56% Mol;-   FD (BFA)=0.10% Mol.

EXAMPLE 11

The procedure was as in Example 10 increasing the quantity of graftingcompound BFA. For the final product the final torque, the degrees ofgrafting FD (MAH) and FD (BFA) were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   1.0 part by weight of BFA-   10 parts by weight of MAH;-   0.4 parts by weight of 2.5 dimethyl, 2.5 diterbutyl peroxy-hexane;-   1 part by weight of BHT.-   Final torque=4.4 Nm;-   FD (MAH)=0.60 mol;-   FD (BFA)=0.36% mol.

EXAMPLE 12 Comparison

The procedure was as in example 10, utilising, however, as graftingsystem only maleic anhydride (MAH). For the final product the finaltorque and FDA (MAH) were noted. Reagent mixture composition:

-   100 parts by weight of polypropylene;-   10 parts by weight of MAH;-   0.4 parts by weight of 2.5 dimethyl 2.5 diterbutyl peroxy-hexane;-   1 part by weight of BHT.-   Final torque=2.9 Nm;-   FD (MAH)=0.43% mol.

By comparing examples 10, 11, and 12, it can be observed that thepolypropylene grafted with the procedure according to the presentinvention (examples 10 and 11) has a higher value of final torque thanthat of the polypropylene grafted according to the prior art only withMAH (Example 12). The addition of BFA in the grafting system is able toreduce the degradation reactions and to determine an increase in thedegree of grafting FD of the polyolefin.

EXAMPLE 13

A discontinuous mechanical Brabender Plastograph OH47055 mixer with amixing chamber of 30 cm³ provided with two rotors was used. The averagetemperature was 180° C. with an overall residence time of 15 minutes.The speed of rotation was fixed at 60 rpm.

Having brought the mixing chamber to the temperature of 180° C. in anitrogen atmosphere, 100 parts by weight (20 g) of polypropylene withMFR (Melt Flow Rate)=0.8 g/10 min were introduced (still maintaining thenitrogen atmosphere), in such a way as entirely to fill the chamber.Having reached a constant torque, 3.5 parts by weight of grafting systemwere introduced, of which 2.7 parts by weight were of maleic anhydride(MAH) in the solid state and 0.8 parts by weight of butylic ester of3-(2-furanyl)-2-propenoic acid (BFA) in the liquid state. After havingreached an adequate homogenisation of the mixture, 0.4 parts by weightof 2,5 dimethyl 2,5 diterbutyl peroxy-hexane were introduced as radicalreaction initiator. At the end of the process 1 part by weight of BHTwas added as an inhibitor of the radical reactions to inhibit anyfurther radical process.

For the final product the final torque and the degrees of grafting FD(MAH) and FD (BFA) were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   0.8 parts by weight of BFA;-   2.7 parts by weight of MAH;-   0.4 parts by weight of 2,5 dimethyl 2,5 diterbutyl peroxy-hexane;-   1 part by weight of BHT.-   Final torque=3.7 Nm;-   FD (MAH)=0.23% mol;-   FD (BFA)=0.12% mol.

EXAMPLE 14 Comparison

The procedure was as in example 13, however utilising as grafting systemonly BFA. For the final product the final torque and FD (BFA) werenoted.

Reagent Mixture Composition:

-   100 parts by weight polypropylene-   0.8 parts by weight BFA-   0.4 parts by weight 2,5 dimethyl 2,5 diterbutyl peroxy-hexane;-   1 part by weight of BHT.-   Final torque=2.6 Nm;-   FD (BFA)=0.16% mol.

EXAMPLE 15

The procedure was as in example 13 increasing the quantity of maleicanhydride (MAH). For the final product the final torque and the degreesof grafting FD (MAH) and FD (BFA) were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   0.8 parts by weight of BFA;-   6 parts by weight of MAH;-   0.4 parts by weight 2,5 dimethyl 2,5 diterbutyl peroxy-hexane;-   1 part by weight of BHT.-   Final torque=4.7 Nm;-   FD (MAH)=0.45 mol;-   FD (BFA)=0.10 mol.

By comparing examples 13, 14 and 15, it can be seen how the associationof MAH and BFA (examples 13 and 15) leads to values of the final torquegreater than those obtained with the use of BFA (in example 14). It canbe concluded that the use of a grafting system comprising MAH and BFApermits a more marked inhibition of the degradation reactions.

EXAMPLE 16

A twin screw extruder with a length/diameter ratio (L/D)=40 and D=35 mmwas used, maintaining a flow rate of 200 kg/h. The extruder is dividedinto 12 sections characterised by different thermal profiles. Theextruder is equipped with a degassing valve in section 10. In the firstsection an average temperature of 90° C. was maintained; from section 2up to section 10 the temperature was 210° C. on average, whilst in thelast two sections 11 and 12 it was maintained on average a temperatureof 200° C.

The test was performed by supplying isotactic polypropylene (MFR=0.8g/10 min) to section 1; in the two successive sections, 2 and 3, thehomogenisation of the polymer took place; the reaction initiator (2,5dimethyl 2,5 diterbutyl peroxy-hexane) and the grafting system, composedby maleic anhydride (MAH) and butylic ester of 3-(2-furfuril) acrylicacid (BFA), was supplied to Section 4.

For the final product the final MFR (evaluated according to the ASTM1238 method) and the degree of grafting FD (MAH) relative to thestarting anhydride groups were noted.

Reagent Mixture Composition:

-   100 parts by weight of polypropylene;-   0.2 parts by weight of BFA;-   2 parts by weight of MAH;-   0.08 parts by weight 2,5 dimethyl 2,5 diterbutyl peroxy-hexane;-   Final MFR=1.7 (g/10 min);-   FD (MAH)=0.60% mol.

EXAMPLE 17 Comparison

The procedure was as in example 16, but no other compound was mixed tothe polypropylene. The final product has a MFR (melt flow rate)=1.0 g/10min.

By comparing the examples 16 and 17, it can be seen how the value of MFRof the two products are comparable, confirming the significant effect ofcontainment of the degradatory reactions by the grafting systemaccording to the invention.

1. A controlled radical grafting process of a polyolefin, derived frommonomeric units comprising α-olefins, comprising the reaction of thepolyolefin and at least one radical reaction initiator with a graftingsystem which comprises at least one grafting compound having an electrondonator heterocyclic aromatic ring conjugated to at least one —HC═CR₁R₂group in which at least one of R₁ and R₂ is an electron acceptorfunctional group, wherein said grafting system further includes at leastone unsaturated compound which has at least one group which reacts withan aminic and/or carboxylic and/or hydroxylic functionality and ischosen from acrylic and methacrylic compounds, maleic anhydride,derivatives ester of maleic anhydride, and their mixtures.
 2. A processaccording to claim 1, in which R₁ and R₂ are chosen independently of oneanother from —H, —COOR, —COOH, —COR, —COH, —CN, —CONH₂, —COO(CH₂)_(n)CF₃and —COO(CH₂)_(n)CN, where R is a linear or branched aliphatic oraromatic linear alkyl group and n is a whole number lying between 1 and20, with the proviso that R₁ and R₂ are not both —H.
 3. A processaccording to claim 1, in which the said heterocyclic ring is asubstituted furanic thiofenic, or pyrrolic ring.
 4. A process accordingto claim 1, in which the said grafting system comprises a compound offormula:

where X is chosen from O, S and N, and R₁ and R₂ are the same ordifferent functional groups chosen from —COOR, —COOH, —COR, —COH, —CN,—CONH₂, —COO(CH₂)_(n)CF₃ and —COO(CH₂)_(n)CN where R is an aliphatic oraromatic linear or branched alkyl group and n is a whole number lyingbetween 1 and
 20. 5. A process according to claim 4, in which the saidgroups R₁ and R₂ are the same of the type —COOR, where R is —CH₂CH₃. 6.A process according to claim 4, in which the said group R₁ is —CN andthe group R₂ is —COOR, where R is —CH₂CH₃.
 7. A process according toclaim 1, in which the said grafting system comprises a compound offormula:

where X is chosen from O, S and N, and R₁ is a functional group chosenfrom —COOR, za-COOH, —COR, —COH, —CN, —CONH₂, —COO(CH₂)_(n)CF₃ and—COO(CH₂)_(n)CN where R is a linear or branched aliphatic or aromaticlinear alkyl group and n is a whole number lying between 1 and
 20. 8. Aprocess according to claim 7, in which the said group R₁ is —COOR, whereR is —CH₂CH₂CH₂CH₃.
 9. A process according to claim 1, in which the saidpolyolefin is chosen from the group consisting of homopolymers andcopolymers of α-olefins and their mixtures.
 10. A process according toclaim 1, in which the said radical initiator has a half life lyingbetween 10 and 200 seconds in the temperature range lying between 120and 240° C.
 11. A process according to claim 1, in which the saidradical initiator is an organic peroxide such as a dialkyl peroxide, adiacil peroxide, a peroxy ester or a peroxychetal.
 12. A processaccording to claim 1 in which the said radical initiator is chosen fromthe group consisting of dicumil peroxide, ditertbutylperoxypropylbenzene,2,5dimethyl2,5ditertbutylperoxy-hexane,3,6,9-triethyl-3,6,9trimethyl-1,4,7triperoxynonan andtheir mixtures.
 13. A process according to claim 1, in which 0.5 to 30%by weight of the said grafting system and from 0.05 to 5 parts by weightof the said radical initiator are mixed with 100 parts by weight of thesaid polyolefin.
 14. A process according to claim 1, in which 100 partsby weight of the said polyolefin are mixed with 1-25 parts by weight ofan unsaturated compound chosen from acrylic and methacrylic compounds,maleic anhydride, ester derivatives of maleic anhydride and theirmixtures, 0.05-5 parts by weight of a radical initiator of organicperoxide type and 0.1-5 parts by weight of a compound of formula

where X can be chosen from O, S and N, and R₁ is a functional groupchosen from COOR, —COOH, —COR, —COH, —CN, —CONH₂, —COO(CH₂)_(n)CF₃ and—COO(CH₂)_(n)CN, where R is a linear or branched aliphatic or aromaticalkyl group and n is a whole number lying between 1 and
 20. 15. Aprocess according to claim 13, in which 100 parts by weight of the saidpolyolefin are further mixed with 0.01-1 parts by weight of a radicalreaction inhibitor.
 16. A process according to claim 15, in which thesaid radical reaction inhibitor is chosen from the group consisting of3,5-di-tert-butyl-4hydroxytoluene,pentaerythrityl-tetrakig[3-(3,5-di-i-butl-4-hydroxlphenyl)-propionate]and actodecyl3,5-di-(tert)-butly-4hydroxhyrocinnamot.
 17. A processaccording to claim 1, performed in a mixer provided with a rotor.
 18. Aprocess according to claim 17, in which the said grafting system isintroduced into the mixer after the polyolefin.
 19. A process accordingto claim 18, in which the said grafting system is introduced into themixer once the torque transmitted by the rotor member is stabilized. 20.A process according to claim 17, in which the said radical initiator isintroduced subsequently to the grafting system.
 21. A process accordingto claim 17, in which the rotor member turns with an angular velocity of20-70 rpm.
 22. A process according to any of claim 17, in which theresidence time of the reagents in the mixer lies between 5 and 30minutes.
 23. A process according to claim 17, in which the temperatureof the reagents lies between 120 and 230° C.
 24. A process according toclaim 17, performed continuously by means of a twin screw extruder. 25.A process according to claim 1, in which the said heterocyclic ring isan unsubstituted furanic thiofenic, or pyrrolic ring.